Grounded transducer for magnetic record disks

ABSTRACT

A transducer particularly for use with magnetic record disks and composed of cores having transducing gaps therein adapted to contact or be in near contact with a record disk at the gaps an composed also of outriggers on the sides of the cores for increasing the surface area of the transducer adapted to contact or be in near contact with a record disk. The cores are of ferrite and have windings thereon, and the outriggers are of ceramic, both the ferrite and ceramic being nonconductive electrically. One of the outriggers is provided with a plating of electrically conductive material on a side surface with the plating being coterminous with the surface of the outrigger adapted to contact the record disk or be in near contact with it, and a ground lead is connected with the plating so as to ground any electrostatic charge on the surface of the disk.

CROSS REFERENCE TO RELATED APPLICATIONS

The invention in this application is related to those in the co-pendingapplication of Norman E. Slindee for Magnetic Disk Drive Unit WithFlexible Skirt, Ser. No. 615,944, filed Sept. 23, 1975 and in co-pendingapplication of Coy L. Huffine et al for Antistatic Magnetic Record DiskAssembly, Ser. No. 615,943, filed Sept. 23, 1975.

BACKGROUND OF THE INVENTION

The invention relates to magnetic disk drives and particularly of thetype adapted to accommodate disk-jacket assemblies. More particularly,the invention relates to mechanism for draining off accumulations ofstatic electricity carried by the jacket and the disk of such anassembly.

Such disk-jacket assemblies have been previously proposed and are incurrent use. Such an assembly is described in the U.S. Pat. No.3,668,658 issued June 6, 1972 to Ralph Flores et al. The assemblydisclosed in this patent includes a magnetic disk which is contained andis rotatably disposed within a square jacket or cover. The jacket has acentral opening for revealing a smaller central opening in the disk bymeans of which the disk can be driven, and the jacket contains twoaligned radially extending slots through which a magnetic transducer mayextend for the purpose of magnetically reading from or writing on asurface of the disk as the disk is rotatably driven.

High electrical resistance materials, such as polyvinyl chlorideacetate, have been found particularly suitable for forming the jacketsin such assemblies. The favorable characteristics of jackets formed withsuch materials are low-cost, resistance to impact, heat sealability forattaching parts of the jackets together to form a complete unit, etc.;however, jackets of such material have been found to accumulate staticelectricity due to normal handling. The disks in such assemblies aregenerally polyethylene terephthalate, also an insulator of highresistivity; and the static electricity also accumulates on the surfacesof the disks. Such accumulations of static electricity would providespurious signals in transducers used with the disks as the staticdischarges; however, if the transducers are of an electricallyconducting type, having their cores formed of iron, for example, theseaccumulations of static electricity are rapidly bled off so that theycause no trouble in ordinary usage of the disk-jacket assemblies.However, it has recently been found very advantageous to use magnetictransducers which are made completely of electrical insulating material.Such a transducer is disclosed in U.S. Pat. No. 3,846,840 issued Nov. 5,1974 and includes ferrite cores having the transducing gaps therein andhaving windings disposed therein for reading, writing or erasinginformation on the associated disk. Such a transducer also includesoutriggers attached to the ferrite cores which are composed of ceramicmaterial. The outriggers are used on the opposite sides of the cores forincreasing the surface of the transducer that makes contact or has aclose air bearing with the disk. Both the ferrite and the ceramicmaterial are of electrically insulating nature and retard the bleedingoff of the accumulated static charge on the jacket and magnetic disk fora very substantial time, such as 15 or 20 minutes. The disk drive thusis rendered incapacitated and unusable for this extended period of time.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide, in connection withsuch a disk drive having a transducer of the type composed ofelectrically insulating materials, improved mechanism which functions tobleed off the static electricity accumulated on such a disk-jacketassembly as previously mentioned.

A preferred form of the invention includes a transducer having a ferritecore with the transducing gaps formed therein, ceramic outriggers fixedwith respect to the core on the sides thereof, a plating on a sidesurface of one of the outriggers of electrically conductive material andterminating at the surface of the transducer adapted to contact themagnetic disk, and a ground lead connected with the plating so that theplating together with the ground lead quickly bleed off the staticelectricity carried by the disk-jacket assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a flexible magnetic disk forming an assemblywith an enclosing envelope which may be used with the apparatus of theinvention (the envelope is partially broken away for more clearlyillustrating the magnetic disk therein);

FIG. 2 is an end elevational view of a disk drive with which theinvention may be used and including a swingable cover for shieldingcertain internal mechanism and for allowing an assembly as shown in FIG.1 to be inserted into the drive;

FIG. 3 is a side elevational view of the internal mechanism of the diskdrive shielded by the cover and taken from one side of the main frame ofthe drive;

FIG. 4 is a sectional view on an enlarged scale taken on line 4--4 ofFIG. 3;

FIG. 5 is a perspective view of a magnetic head assembly embodying theprinciples of the invention and including an outrigger at the forefrontof the figure which is plated with an electrically conductive materialand is grounded in accordance with the teachings of the invention;

FIGS. 6 and 7 are respectively end and side views of the platedoutrigger just mentioned;

FIG. 8 is a sectional view of a pair of the magnetic head assemblies ofthe invention disposed opposite each other and on opposite sides of thedisk of the FIG. 1 assembly; and

FIG. 9 is a sectional view of a modified magnetic head assembly andembodying the principles of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1 in particular, the magnetic disk assembly 18, whichmay be utilized by a disk drive including the magnetic heads andgrounding apparatus therefor of the invention, may be seen to comprise amagnetic disk 20 disposed within a square envelope 22. The disk 20 is ofa thin, flexible material, such as polyethylene terephthalate of about0.003 inch thickness; and the disk 20 has an unoriented Fe₂ O₃ coatingon both sides. The envelope 22 may be of a more rigid, but stillsomewhat flexible, vinyl sheet material of 0.010 inch thickness, forexample. The disk 20 has a central opening 24, and the envelope 22 haslarger central openings 26 in its two thicknesses. In addition, theenvelope 22 has aligned radial slots 28 and aligned round openings 30 inits two thicknesses. The openings 30 are adapted to align with anopening 32 in the disk 20 as the disk 20 rotates within the envelope 22.An assembly of this type is disclosed in U.S. Pat. No. 3,668,658, issuedJune 6, 1972, which may be referred to for more detail of the assembly.

A disk drive for use with the disk assembly 18 and which includes theimproved magnetic heads and grounding apparatus of the invention isdisclosed basically in FIGS. 2-4 hereof and is disclosed basically ingreater detail in the co-pending U.S. patent application of Daniel O.Castrodale et al, Ser. No. 570,118, filed Apr. 21, 1975 for Data StorageApparatus Using A Flexible Magnetic Disk, which application may bereferred to for greater detail of the disk drive. Referring to FIGS.2-4, the disk drive may be seen to include a backbone or frame assembly34 which as shown in FIG. 3 is connected to the ground 35 of the systemusing the disk drive. The frame assembly 34 has a cover 36 swingablymounted thereon by means of pivots 38 and is formed with downwardlytapering slots 40 for receiving a disk assembly 18. The frame assembly34 is provided with a pair of stops 42 (see FIG. 3) on opposite sidesfor limiting the downward movement of the assembly 18 within the slots40 and has a protruding platen portion 44 (see FIG. 4) for supporting aface of the envelope 22 as will be hereinafter described. A shaft 46 isrotatably disposed in the frame assembly 34 and is formed with a driverim or flange portion 48 and with a central countersunk depression 50 inone end of the shaft 46. A pulley 52 is fixed on the other side of theshaft 46, and the pulley 52 is driven from a drive motor 54 located onthe bottom of the frame assembly 34, the drive being by means of a belt56 which extends around the pulley 52 and around the output pulley 58 ofthe motor 54.

The cover 36 has a tapered collet 66 rotatably mounted therein andloaded by a spring 68, and the collet 66 is adapted to enter thecountersunk depression 50 in the end of the shaft 46 when the cover 36is swung toward the frame assembly 34 so as to capture a disk 20 betweenthe collet 66 and rim 48 for driving the disk. Any suitable latchingmeans may be used for holding the cover 36 in closed dispositionclamping a disk 20 between the collet 66 and the rim 48.

A carriage 70 is slideably disposed in the frame assembly 34 in such amanner as to move toward and away from the center of shaft 46. Thecarriage 70 embraces the disk assembly 18 resting on the stops 42 andhas one part 72 on one side of the disk assembly 18 and has a secondpart 74 fixed with respect to the part 72 and disposed on the other sideof the disk assembly 18. A pair of guide rods 76 and 78 are fixed withrespect to the frame assembly 34 and extend through openings 80 and 82in the part 74 for guiding the carriage 70 radially with respect to thecenter of the shaft 46. Carriage 70 may be moved radially with respectto shaft 46 by means of a flexible steel band 86 that extends around adrive pulley 88 and around an idler pulley 90. The band 86 is fixed withrespect to carriage 70 by any suitable clamping means, and pulley 88 isdriven from any suitable drive motor (not shown).

Swing arms 104 and 106 are respectively disposed within openings 72a and74a in the parts 72 and 74. The swing arms 104 and 106 are connectedwith the carriage 70 by means of leaf springs, such as the leaf spring108 for the swing arm 104; and the leaf springs are fixed with respectto the lower end of the carriage 70 by means of threaded bolts 112 andnuts 114. The swing arms 104 and 106 are yieldably moved together bymeans of leaf return springs, such as the leaf return spring 118effective on swing arm 104.

An electromagnet 130 (see FIG. 4) is provided for swinging the arm 104outwardly; and any suitable mechanical connection may be providedbetween the arms 104 and 106, such as that disclosed in said Castrodaleet al application, for causing the arm 106 to swing outwardly at thesame time as the arm 104. The electromagnet 130 has a core 132, and anarmature 134 moves toward and away from the core 132. The armature 134is in the form of a lever which is fulcrumed in an opening 136 in astandard 138 that is fixed with respect to the frame assembly 34. Aspring 140 is provided between the standard 138 and the lever 134. Alever extension 142 of relatively thin flexible material is fixed at itsbase end to the lever 134, and an adjustment screw 144 is provided foradjusting the extension 142 with respect to the armature 134. The leverextention 142 carries a foam rubber pressure member 146 that is locatedopposite the platen portion 44 of the frame assembly 34. The leverextension 142 also has a shorter but elongate end portion 142a that isdisposed beneath a hook 148 fixed to the outer surface of the swing arm104.

Swing arms 104 and 106 respectively carry electromagnetic heads ortransducers 250 and 252 which, together with the grounding meanstherefore, incorporate the principles of the invention. The transducer250 is fixed with respect to the arm 104 by means of a leaf spring 176,and a load arm 182 is fixed with respect to the leaf spring 176. Hookportions 104b integral with arm 104 extend around load arm 182 fordrawing transducer 250 out of engagement with disk 20 when arm 104 isswung outwardly with respect to carriage 70 by de-energization ofelectromagnet 130. Transducer 252 is mounted in a similar manner withrespect to arm 106 using a leaf spring 184 corresponding to the leafspring 176, and hook portions 106b overlying load arm 186 withdrawtransducer 252 from engagement with disk 20 when arm 106 is swungoutwardly away from disk 20. Further details of suitable mountings fortransducers 250 and 252 with respect to arms 104 and 106 may be had byreferring to said Castrodale et al application, Ser. No. 570,118.

The magnetic transducer 250 is illustrated in FIG. 5 and on the left ofthe disk 20 in FIG. 8. The transducer 252 is identical with thetransducer 250 but is simply turned through 180°. The transducers 250and 252 are basically the transducer which is disclosed in U.S. Pat. No.3,846,840, issued Nov. 5, 1974, but the transducers 250 and 252 haveimproved grounding devices for the disk 20.

The transducers 250 and 252 are suitable for reading and/or writing atrack of magnetic information on disk 20 and for erasing the edges ofthe track as well as old information adjacent the edges of the newlywritten track after it is written. Referring to FIG. 5, the transducer250 includes a read/write core layer 240 centrally disposed betweenouter erase core layers 242 and 243, with the base surfaces thereofhaving the read/write transducing gap 227 and the erase transducing gaps237 and 238 respectively, being coplanar in transducer surface X whichis that surface of transducer 250 that makes contact with disk 20 or mayhave a very thin air bearing with disk 20 for information transferbetween transducer 250 and disk 20. A read/write coil 246 is disposedaround the end leg of the read/write core, and a single erase coil 247is disposed over the end legs of the pair of erase cores 242 and 243.The coils are energized by an appropriate current source which iswell-known in the art. A sidebar 245 bridges the legs of the magneticcore of the middle layer so as to provide a low reluctance flux paththrough the read/write core. A sidebar is not needed across the legs ofthe erase cores, since sufficient flux is produced across the erasetranducing gaps by the erase coil 247 to erase the edges of theread/write track. Nonmagnetic outrigger portions 248 and 249 are securedto the outer sides of the erase cores 242 and 243, with the basesthereof being coplanar with the base surface X of the transducerassembly. The outriggers protect the erase cores from erosion andincrease the bearing area of surface X, thus assuring a constant erasegap and uniform wear of the head assembly. The outrigger 249 has alongitudinal groove 249a therein, and this groove extends in the samedirection A as the disk 20 moves across the transducer 250.

The outrigger 248 has a flat base surface 248a that extends parallelwith disk 20 and is a part of surface X, an opposite outer surface 248b,end surfaces 248c and 248d and side surfaces 248e and 248f. Theoutrigger 248 is also formed with curved edge portions 248g, 248h and248j. As will be observed from FIGS. 6 and 7 in particular, the surfaces248b, 248c, 248d, 248e and 248F are provided with a layer or coating xthereon, and this is a plating of electrically conducting material, suchas copper. The beveled corners 248g, 248h and 248j have no such layerthereon, but the conductive layer on the surface 248e extends all theway down to the transducer surface X that is in contact with disk 20except possibly for the air bearing of minute thickness between theoutrigger 248 and disk 20. The transducer 250 as seen in FIG. 8 isbonded with respect to the spring 176 by means of an adhesive body 290which may be an electrically conductive epoxy to thus connect thecoating x on the outrigger 248 to the spring 176. The spring 176 is ofmetal and thus electrically conducting and is connected by means of aflexible electrically conducting cable 292 to the ground 35 for thesystem with which the disk drive is used. Since both frame 34 and cable292 are connected to ground 35, cable 292 is thus effectively connectedto the frame assembly 34. The cable 292 is fixed by means of a body ofconductive epoxy 294 to the spring 176. Since the corners 248g, 248h and248j are rounded, the plating x on the surfaces 248d, 248c and 248f isnot in close proximity to the adjacent surface of the disk 20 (see FIGS.6 and 7), but the surface 248e of the outrigger 248 is internal in thetransducer and is in contact with the ferrite core 242; and the layer xon this surface 248e ends and is coterminous with the plane of surface Xthat is lapped on the transducer 250 as will be described.

As previously mentioned, the transducer 252 is identical with thetransducer 250 but is simply turned through 180°. The groove 249a in thetransducer 252 is therefore out of line with the groove 249a in thetransducer 250, as these transducers are illustrated in FIG. 8. Thetransducer 252 is bonded to the leaf spring 184 by a body 296 ofconductive epoxy, and a body 298 of conductive epoxy connects the leafspring 184 with a conductor cable 299. The conductive bodies 296 and 298correspond to the conductive bodies 290 and 294 used for the transducer250, and the cable 299 is similar to the cable 292 and is also connectedto system ground 35 for grounding the electrically conducting coatingson the transducer 252 with respect to the frame assembly 34 in the samemanner as the conducting coatings on the transducer 250 are groundedwith respect to the frame assembly 34.

In the operation of the disk drive, the disk-jacket assembly shown inFIG. 1 is inserted into the slots 40. The cover 36 is then swung closedabout its pivots 38 so as to clamp the disk 20 between the collet 66 andthe drive rim 48. The motor 54 then functions to drive the disk 20through the belt 56, and the transducers 250 and 252 are moved intocontact (or very near floating contact) with opposite surfaces of thedisk 20. The transducer gaps 227, 238 and 237, utilizing the coils 245and 247, may then be used for either writing, reading or erasing on thedisk 20, using the coils 246 and 247 appropriately, as is well-known inthe art.

As has been previously explained, a disk-jacket assembly 18 of the typeshown in FIG. 1 and used in the disk drive accumulates staticelectricity due to normal handling; and this may be expected to occurbefore the disk-jacket assembly is inserted into the disk drive. Thischarge of static electricity could be expected to interfere particularlywith reading information from the disk 20 for a substantial period oftime, were it not for the grounding action provided by the electricallyconducting coating x on the outrigger surface 248e and the groundinglead 292 connected thereto through the spring 176 (the grounding actionof the transducer 252 is the same, utilizing the grounding lead 299).Since the outriggers 248 and 249 and the cores 240, 242 and 243 are allof electrically insulating material, they cannot provide a ground to thesurface of the disk 20 for this action. Although apparently the chargeon the assembly 18 is on the jacket 22, an opposite charge apparentlyaccumulates on the disk 20 when it is inserted in the drive and isconducted to the transducer 252 by the rotation of disk 20 which is incontact with the coating x on the outrigger surface 248e so that thecharge is quickly grounded with respect to system ground 35 and frameassembly 34 via this coating x and the ground lead 292.

The cores 240, 242 and 243 having the windings 245 and 247 thereon andhaving the transducing gaps 227, 237 and 238 therein are composed of aniron nickel zinc ferrite as mentioned in said U.S. Pat. No. 3,846,840.The ferrite is of electrically insulating material and is used in placeof the prior used electrically conducting metal in transducers, becausesuch ferrite heads are less costly and provide better reading response.The outriggers 248 and 249 are the baria titania ceramic mentioned forthe outriggers in U.S. Pat. No. 3,846,840, and this material is alsoelectrically insulating. This ceramic material is used for theoutriggers 248 and 249 for two reasons: (1) the ceramic has the samelapping rate as the ferrite and (2) the ceramic has substantially thesame thermal coefficient of expansion as the ferrite of the cores 240,242 and 243.

The surface X of the transducer 250 adapted to contact the disk,including the surface 248a of the outrigger 248, is lapped so as to beaccurately planar. This is important if the transducer 250 is to have avery intimate contact with the disk 20 as the disk 20 rotates, and thisintimate contact is necessary if high density recording is to beattained. If the materials of the cores 240, 242 and 243 and of theoutriggers 248 and 249 have different lapping rates, the surface X ofthe transducer 250 adapted to make contact with the disk 20 could not belapped to be absolutely flat-- hence it is important that the materialsof the outriggers and of the cores have the same lapping rate. This isattained by making the outriggers 248 and 249 of ceramic, with the cores240, 242 and 243 being ferrite.

As is explained in U.S. Pat. No. 3,846,840, the parts of the transducerthere described are bonded together by glasses which must be heated to600° centigrade to 700° centigrade in order that the glasses may meltand bond the parts of the transducer together. The transducers 250 and252 are the same as the transducer described in this patent in thisrespect; and, if the materials of the cores 240, 242 and 243 and of theoutriggers 248 and 249 did not have the same thermal coefficient ofexpansion, the glass bonds of these transducers would be broken as thetransducer cooled after being heated for causing the glasses to flowbetween and bond the parts of the transducers together. Making the coresof ferrite and making the outriggers of ceramic satisfy thisrequirement, since the ceramic and ferrite have substantially the samecoefficients of expansion. The glass is used particularly for bondingthe cores 240, 242 and 243 together, and the glass exists in the gaps238, 237 and 227 in particular. An epoxy cement may be used for fixingthe outriggers 248 and 249 onto the cores 242 and 243 if desired;however, the same breakage would occur to the epoxy bonds as to theglass bonds if the coefficients of expansion of the materials of theoutriggers and cores were not the same. There is still another reasonwhy the thermal coefficients of expansion of all parts of the transducer250 should be the same, and this is due to the fact that if the ferriteof the cores has a stress put on it due to unequal expansions, itsmagnetic permeability changes undesirably. In a practical application ofthe transducer 250, its temperature during usage, shipping and storagemay change as much as 100 degrees centrigrade; and such temperaturechange could cause a change in permeability if the outriggers andmagnetic cores do not have substantially the same coefficients ofexpansion.

In the manufacture of the transducer 250, the parts are all bondedtogether to form the complete transducer as is shown in FIG. 5, with theglass and epoxy bonding holding the cores 240, 242 and 243 and theoutriggers 248 and 249 together. The outrigger 248, prior to theassembly of the transducer 250 and prior to lapping of the transducer onits surface X contacting the disk 20 and including the surface 248a ofthe outrigger 248, has been plated with an electrically conductive metalon all surfaces. The transducer 250 is then lapped on its surface Xadapted to contact the disk 20, and the surface X is made accuratelyflat by this lapping operation particularly since the lapping rate ofthe ceramic and of the ferrite are the same. The corners 248g, 248h and248j are then rounded so that the outriggers do not tend to abrade thesurface of the disk 20 on which the transducer is applied.

FIG. 9 discloses a modification of the invention and particularly amodified form of transducer 300 which is adapted to be used with a disk20 that is supported by a felt pressure pad 302 positioned on the sideof the disk 20 opposite that on which the transducer 300 is positioned.A disk drive of this type is disclosed in U.S. Pat. No. 3,846,836 issuedNovember 5, 1974, and the transducer 300 and pressure pad 302respectively correspond with the transducer 124 and the pressure padassembly 128 in the disk drive of U.S. Pat. No. 3,846,836.

The core assembly 304 of transducer 300 may correspond with the coreassembly of transducer 250 including the cores 242, 243 and 240; and thetransducer 300 has two outriggers 306 and 308 on the opposite sides ofthe core assembly 304. The outrigger and transducer surfaces 304a, 306aand 308a that are adjacent the disk 20 and are opposite the pressure pad302 together form a spherical surface Y opposite pad 302. The othersurfaces of the outriggers 306 and 308 are plated with electricallyconductive layers y and z respectively, and an electric lead 314connects the conductive layers on the two outriggers 306 and 308. Aground wire 316 is connected to the plating z on the outrigger 308 andis grounded to system ground 35 in the same manner as is the lead 292 ofthe previously described embodiment.

The grounding action by the electrically conducting coatings y and z onthe outriggers 306 and 308 is substantially the same as described inconnection with the transducer 250. The transducer 300, however, differsfrom the transducer 250 in that the transducer 300 has the surfaces308a, 304a and 306a which compositely form spherical surface Y so as toaccommodate to the relatively soft pressure pad 302. The surfaces 308a,304a and 306a are lapped to have this spherical shape, and it isimportant if the shape is to be accurately spherical that the outriggers308 and 306 be of ceramic so as to have the same lapping rate as theferrite of the core 304. The outriggers 306 and 308, like the outrigger248, are initially plated on all of their surfaces; and the lapping ofthe surfaces 308a and 306a removes the plating from the outriggers 308and 306 on these surfaces. The plating remains on the other surfaces ofthe outriggers 308 and 306, and the ends of the plating layers y and zare coterminous, on the same spherical surface Y with the surfaces 308a,304a and 306a. The disk 20 may curve slightly around the transducer 300due to the action of the felt pad 302; nevertheless, the surface of thedisk 20 can be expected to be in contact with at least one of the twoconductive layers z₁ and y₁ on the transducer 300 which are coterminouswith the arcuate surface Y and are next to the core assembly 304. Theplated layers on the outriggers 306 and 308 are grounded by the lead316, and the plated layers on the outriggers 308 and 306 thus rapidlyconduct off any accumulations of static electricity on the disk-jacketassembly 18 in the same manner that the plated layer x on the outriggersurface 248e is effective for the transducer 250.

We claim:
 1. A magnetic head assembly for cooperating with a relativelymoving magnetic medium comprising:a read-write core of electricallyinsulating and magnetically permeable material having a transducer gapin a contact surface of the head assembly adapted to contact or have athin air bearing with the magnetic medium, a read-write winding on saidcore, an erase core of electrically insulating and magneticallypermeable material having first and second opposite sides and bonded onits first side to said read-write core and having a transducer gap insaid contact surface, an erase winding on said erase core, and a thinlayer of electrically conducting material disposed on said second sideof said erase core which is remote from said read-write core andextending away from and terminating on said contact surface of the headassembly so that static electricity carried by the magnetic medium maybe conducted off of the medium through said layer.
 2. A magnetic headassembly for cooperating with a relatively moving magnetic mediumcomprising;a ferrite read-write core having a transducer gap in acontact surface of the head assembly adapted to contact or have a thinair bearing with the magnetic medium, a read-write winding on said core,a ferrite erase core having first and second opposite sides and bondedon its first side to said read-write core and having a transducer gap insaid contact surface, an erase winding on said erase core, an outriggerof ceramic material disposed on said second side of said erase corewhich is remote from said read-write core, and a thin layer ofelectrically conducting material disposed between said outrigger andsaid erase core and extending away from and terminating on said contactsurface of the head assembly so that static electricity carried by themagnetic medium may be conducted off of the medium through said layer.3. A magnetic head assembly as set forth in claim 2, said contactsurface being a plane surface.
 4. A magnetic head assembly as set forthin claim 2, said contact surface being a spherical surface.
 5. Amagnetic head assembly as set forth in claim 2, said thin layer ofelectrically conducting material constituting a metal plating on asurface of said outrigger which is adjacent to said second side of saiderase core.
 6. A magnetic head assembly as set forth in claim 5, saidcores being fixed together by means of a bonding material and saidplating and thereby said outrigger being fixed with respect to saiderase core by means of a bonding material,said layer of electricallyconducting material having a height measured off and away from saidcontact surface which is substantially less than the height of saiderase core measured from said contact surface.